The correct answer is B) oil fires in the engine room bilges. Aqueous Film Forming Foam (AFFF), or 'light water', is especially suitable for fighting oil fires. AFFF is effective at extinguishing and preventing the re-ignition of flammable liquid fires, such as those that may occur in engine room bilges on ships. AFFF works by forming an aqueous film that rapidly cuts off the oxygen supply to the fire, effectively smothering it. The other answer choices are incorrect because: A) AFFF is not the most suitable agent for class D (combustible metal) fires; C) AFFF is not the primary agent for fighting class C (energized electrical) fires in paint lockers; and D) AFFF is not the best agent for all fire classes, as indicated in the explanation for A) and C).